Seems the best choice is going to prison and getting banished from court with Anna pissed off at you. At least Syanna gets what was coming to her and Detlaff and Regis can go live in peace.
During some bold exploration activies into the palace grounds that I did yesterday after the good ending (Detlaff lives = Regis won't suffer; psychopath criminal sister is dead, prison, etc), I found Anarietta and Damien in the palace grounds. In a little pavillon near the place where the palace interaction cutscenes happened earlier.
I could interact with both. Some longer dialogue options with Anarietta; just a normal and non-hostile one-line response from Damien. I was not thrown back into prison for having dared to approach them, I was not thrown out of the palace grounds. Anarietta was fully coherent and normal again. Already done with the grief about the death of the sister for whom she didn't really ever show greater concern for anyway.
This is absolutely the best ending.
My path to it was:
- told Regis that I didn't know which path I wanted to chose, so he went and saved innocent people while I was thinking about it
- killed a lot of vampires on the way down and saved a few people
- went with Orianna before meeting Damien at the bank
- did Orianna's quest
- talked with the ravens
- walked to the docks, killing some more rampaging vampires on the way, thus saving some more innocents
- went with Regis to get Syanna
- rejoiced in the dialogue options that did not please Syanna in Wonderland
- let Detlaff go. Yeah, Regis got his point across.
- got the prison poster, won in Gwent and wondered how exactly Geralt picks flowers/mushrooms/stuff.
- investigated the 5th letter
- decided not to tell Anarietta about it (will tell Dandelion about it, later. He's staying in Touissant for a while, so there will be some opportunity.)
- explored a little bit more afterwards. Looks like the psycho sister didn't get any particularly great tomb in the graveyard. And found Anarietta back in normal mental state. Yay.
And I have the option now to get the gauntlets and do a tiny bit of exploration in the Elder's Cave. Hurray.
This all felt really nice.